Pass TraceIterator to JIT compilers rather than Vec<TracedAOTBlock>.

This allows the JIT compilers, if they so choose, to iterate over the
blocks. If a tracer chooses to process (e.g. decode) its trace in a
thread, this means that (some of) compilation and trace processing can
occur in parallel.

At the moment, this commit doesn't change anything meaningful inside
jitc_ykllvm or jitc_yk: both immediately `collect` the iterator into a
`Vec`. But the API is now flexible enough to allow something better in
the future.

ykrt/src/compile/jitc_llvm.rs

@@ -5,7 +5,7 @@ use crate::{
     compile::{CompilationError, CompiledTrace, Compiler},
     location::HotLocation,
     mt::{SideTraceInfo, MT},
-    trace::TracedAOTBlock,
+    trace::{TraceIterator, TracedAOTBlock},
 };
 use object::{Object, ObjectSection};
 use parking_lot::Mutex;
@@ -32,10 +32,11 @@ impl Compiler for JITCLLVM {
     fn compile(
         &self,
         mt: Arc<MT>,
-        irtrace: Vec<TracedAOTBlock>,
+        aottrace_iter: Box<dyn TraceIterator>,
         sti: Option<SideTraceInfo>,
         hl: Arc<Mutex<HotLocation>>,
     ) -> Result<CompiledTrace, CompilationError> {
+        let irtrace = aottrace_iter.collect::<Vec<_>>();
         let (func_names, bbs, trace_len) = self.encode_trace(&irtrace);
 
         let llvmbc = llvmbc_section();

ykrt/src/compile/jitc_yk/mod.rs

@@ -5,7 +5,7 @@ use crate::{
     compile::{CompiledTrace, Compiler},
     location::HotLocation,
     mt::{SideTraceInfo, MT},
-    trace::TracedAOTBlock,
+    trace::TraceIterator,
 };
 use parking_lot::Mutex;
 use std::{
@@ -60,7 +60,7 @@ impl Compiler for JITCYk {
     fn compile(
         &self,
         _mt: Arc<MT>,
-        mtrace: Vec<TracedAOTBlock>,
+        aottrace_iter: Box<dyn TraceIterator>,
         sti: Option<SideTraceInfo>,
         _hl: Arc<Mutex<HotLocation>>,
     ) -> Result<CompiledTrace, CompilationError> {
@@ -77,6 +77,7 @@ impl Compiler for JITCYk {
             eprintln!("--- End aot ---");
         }
 
+        let mtrace = aottrace_iter.collect::<Vec<_>>();
         let jit_mod = trace_builder::build(&aot_mod, &mtrace)?;
 
         if PHASES_TO_PRINT.contains(&IRPhase::PreOpt) {

ykrt/src/compile/mod.rs

@@ -1,7 +1,7 @@
 use crate::{
     location::HotLocation,
     mt::{SideTraceInfo, MT},
-    trace::TracedAOTBlock,
+    trace::TraceIterator,
 };
 use libc::c_void;
 use parking_lot::Mutex;
@@ -41,7 +41,7 @@ pub(crate) trait Compiler: Send + Sync {
     fn compile(
         &self,
         mt: Arc<MT>,
-        irtrace: Vec<TracedAOTBlock>,
+        aottrace_iter: Box<dyn TraceIterator>,
         sti: Option<SideTraceInfo>,
         hl: Arc<Mutex<HotLocation>>,
     ) -> Result<CompiledTrace, CompilationError>;

ykrt/src/mt.rs

@@ -484,7 +484,6 @@ impl MT {
         let mt = Arc::clone(self);
         let do_compile = move || {
             mt.stats.timing_state(TimingState::TraceMapping);
-            let irtrace = trace_iter.collect::<Vec<_>>();
             debug_assert!(
                 sidetrace.is_none() || matches!(hl_arc.lock().kind, HotLocationKind::Compiled(_))
             );
@@ -497,7 +496,7 @@ impl MT {
             let guardid = sidetrace.as_ref().map(|x| x.0.guardid);
             match compiler.compile(
                 Arc::clone(&mt),
-                irtrace,
+                trace_iter,
                 sidetrace.as_ref().map(|x| x.0),
                 Arc::clone(&hl_arc),
             ) {